Chapter 42: Gas Exchange 1.Why is gas exchange important? -Aerobic organisms need O 2 for oxidative phosphorylation (making ATP) -CO 2 from citric acid cycle must be removed

Figure The role of gas exchange in bioenergetics Organismal level Cellular level Circulatory system Cellular respiration ATP Energy-rich molecules from food Respiratory surface Respiratory medium (air or water) O2O2 CO 2

Chapter 42: Gas Exchange 1.Why is gas exchange important? -Aerobic organisms need O 2 for oxidative phosphorylation (making ATP) -CO 2 from citric acid cycle must be removed 2.How have gas exchange systems changed as animals evolved? -Small, thin organisms – diffusion directly across skin -Larger organisms need a larger surface area (gills, trachea or lungs)

Figure Diversity in the structure of gills, external body surfaces functioning in gas exchange (a) Sea star. The gills of a sea star are simple tubular projections of the skin. The hollow core of each gill is an extension of the coelom (body cavity). Gas exchange occurs by diffusion across the gill surfaces, and fluid in the coelom circulates in and out of the gills, aiding gas transport. The surfaces of a sea star’s tube feet also function in gas exchange. (b) Marine worm. Many polychaetes (marine worms of the phylum Annelida) have a pair of flattened appendages called parapodia on each body segment. The parapodia serve as gills and also function in crawling and swimming. (d) Crayfish. Crayfish and other crustaceans have long, feathery gills covered by the exoskeleton. Specialized body appendages drive water over the gill surfaces. (c) Scallop. The gills of a scallop are long, flattened plates that project from the main body mass inside the hard shell. Cilia on the gills circulate water around the gill surfaces. Gills Gill Parapodia Gills Tube foot Coelom

Chapter 42: Gas Exchange 1.Why is gas exchange important? -Aerobic organisms need O 2 for oxidative phosphorylation (making ATP) -CO 2 from citric acid cycle must be removed 2.How have gas exchange systems changed as animals evolved? -Small, thin organisms – diffusion directly across skin -Larger organisms need a larger surface area (gills, trachea or lungs) 3. How have fish gills evolved for maximal gas exchange?

Figure The structure and function of fish gills Gill arch Water flow Operculum Gill arch Blood vessel Gill filaments Oxygen-poor blood Oxygen-rich blood Water flow over lamellae showing % O 2 Blood flow through capillaries in lamellae showing % O 2 Lamella Countercurrent exchange 100% 40% 70% 15% 90% 60% 30% 5% At best, concurrent exchange would give blood O 2 of 50%. Fish expend lots of energy ventilating – forcing water across gills to get O 2.

Chapter 42: Gas Exchange 1.Why is gas exchange important? -Aerobic organisms need O 2 for oxidative phosphorylation (making ATP) -CO 2 from citric acid cycle must be removed 2.How have gas exchange systems changed as animals evolved? -Small, thin organisms – diffusion directly across skin -Larger organisms need a larger surface area (gills, trachea or lungs) 3.How have fish gills evolved for maximal gas exchange? 4.Why don’t gills work on land? -Too dry for gills large surface area -External gas exchange will not occur 5.What adaptations do land animals have? -Internal exchange -Tracheal systems with many openings (spiracles)

Figure Tracheal systems Spiracle Tracheae Air sacs Air sac Body cell Air Trachea Tracheole Tracheoles Mitochondria Myofibrils Body wall 2.5 µm (a) The respiratory system of an insect consists of branched internal tubes that deliver air directly to body cells. Rings of chitin reinforce the largest tubes, called tracheae, keeping them from collapsing. Enlarged portions of tracheae form air sacs near organs that require a large supply of oxygen. Air enters the tracheae through openings called spiracles on the insect’s body surface and passes into smaller tubes called tracheoles. The tracheoles are closed and contain fluid (blue-gray). When the animal is active and is using more O 2, most of the fluid is withdrawn into the body. This increases the surface area of air in contact with cells. (b) This micrograph shows cross sections of tracheoles in a tiny piece of insect flight muscle (TEM). Each of the numerous mitochondria in the muscle cells lies within about 5 µm of a tracheole.

Chapter 42: Gas Exchange 1.Why is gas exchange important? 2.How have gas exchange systems changed as animals evolved? 3.How have fish gills evolved for maximal gas exchange? 4.Why don’t gills work on land? 5.What adaptations do land animals have? -Internal exchange -Tracheal systems with many openings (spiracles) -Lungs in spiders, terrestrial snails & vertebrates -1 location for opening -Dense net of capillaries 6.What is the flow of air in our respiratory system? Nostrils  nasal cavity  pharynx  larynx  trachea  Bronchi  bronchioles  alveoli

Branch from the pulmonary vein (oxygen-rich blood) Terminal bronchiole Branch from the pulmonary artery (oxygen-poor blood) Alveoli Colorized SEM SEM 50 µm Heart Left lung Nasal cavity Pharynx Larynx Diaphragm Bronchiole Bronchus Right lung Trachea Esophagus Figure The mammalian respiratory system - Mostly lined with cilia & thin layer of mucus

Chapter 42: Gas Exchange 1.Why is gas exchange important? 2.How have gas exchange systems changed as animals evolved? 3.How have fish gills evolved for maximal gas exchange? 4.Why don’t gills work on land? 5.What adaptations do land animals have? 6.What is the flow of air in our respiratory system? 7.What is the difference between positive & negative breathing? -Positive – tongue pushes air down into lungs – frogs -Negative – air pulled down into lungs - us

Figure Negative pressure breathing Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax Air inhaled Air exhaled INHALATION Diaphragm contracts (moves down) EXHALATION Diaphragm relaxes (moves up) Diaphragm Lung Thoracic cavity expands & air is forced into nose. Muscles relax & thoracic cavity gets smaller and air is forced out of nose.

Chapter 42: Gas Exchange 1.Why is gas exchange important? 2.How have gas exchange systems changed as animals evolved? 3.How have fish gills evolved for maximal gas exchange? 4.Why don’t gills work on land? 5.What adaptations do land animals have? 6.What is the flow of air in our respiratory system? 7.What is the difference between positive & negative breathing? 8.How is breathing controlled? (oxygen homeostasis) -Medulla oblongata & pons -O 2 sensors in aorta & carotids & CO 2 sensors in carotids

Pons Breathing control centers Medulla oblongata Diaphragm Carotid arteries Aorta Cerebrospinal fluid Rib muscles The control center in the medulla sets the basic rhythm, and a control center in the pons moderates it, smoothing out the transitions between inhalations and exhalations. Nerve impulses trigger muscle contraction. Nerves from a breathing control center in the medulla oblongata of the brain send impulses to the diaphragm and rib muscles, stimulating them to contract and causing inhalation. In a person at rest, these nerve impulses result in about 10 to 14 inhalations per minute. Between inhalations, the muscles relax and the person exhales. The medulla’s control center also helps regulate blood CO 2 level. Sensors in the medulla detect changes in the pH (reflecting CO 2 concentration) of the blood and cerebrospinal fluid bathing the surface of the brain. Nerve impulses relay changes in CO 2 and O 2 concentrations. Other sensors in the walls of the aorta and carotid arteries in the neck detect changes in blood pH and send nerve impulses to the medulla. In response, the medulla’s breathing control center alters the rate and depth of breathing, increasing both to dispose of excess CO 2 or decreasing both if CO 2 levels are depressed. The sensors in the aorta and carotid arteries also detect changes in O 2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low Figure Automatic control of breathing

Chapter 42: Gas Exchange 1.Why is gas exchange important? 2.How have gas exchange systems changed as animals evolved? 3.How have fish gills evolved for maximal gas exchange? 4.Why don’t gills work on land? 5.What adaptations do land animals have? 6.What is the flow of air in our respiratory system? 7.What is the difference between positive & negative breathing? 8.How is breathing controlled? (oxygen homeostasis) 9.How are gases exchanged across selectively permeable membranes? - Simple diffusion

Inhaled airExhaled air O2O2 CO 2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O CO 2 O2O2 Alveolar epithelial cells Pulmonary arteries Blood entering alveolar capillaries Blood leaving tissue capillaries Blood entering tissue capillaries Blood leaving alveolar capillaries CO 2 O2O2 Tissue capillaries Heart Alveolar capillaries of lung 45 Tissue cells Pulmonary veins Systemic arteries Systemic veins O2O2 CO 2 O2O2 Alveolar spaces Figure Loading and unloading of respiratory gases

Chapter 42: Gas Exchange 1.Why is gas exchange important? 2.How have gas exchange systems changed as animals evolved? 3.How have fish gills evolved for maximal gas exchange? 4.Why don’t gills work on land? 5.What adaptations do land animals have? 6.What is the flow of air in our respiratory system? 7.What is the difference between positive & negative breathing? 8.How is breathing controlled? (oxygen homeostasis) 9.How are gases exchanged? 10. How is the O 2 carried in the blood? - By hemoglobin in RBCs

Figure Hemoglobin loading and unloading O 2 Heme group Iron atom O 2 loaded in lungs O 2 unloaded In tissues Polypeptide chain O2O2 O2O2 1 RBC has 250 million Hb molecules X 4 O 2 molecules = 1 billion O 2 per RBC X 25 trillion RBC per person = 1 billion O 2 per RBC 2.5 x O 2 total Cooperativity works in loading & unloading of O 2. RBC do not have a nucleus so more room for Hb.

Chapter 42: Gas Exchange 1.Why is gas exchange important? 2.How have gas exchange systems changed as animals evolved? 3.How have fish gills evolved for maximal gas exchange? 4.Why don’t gills work on land? 5.What adaptations do land animals have? 6.What is the flow of air in our respiratory system? 7.What is the difference between positive & negative breathing? 8.How is breathing controlled? (oxygen homeostasis) 9.How are gases exchanged? 10. How is the O 2 carried in the blood? 11. How is O 2 dumped from hemoglobin?

Figure Dissociation curves for hemoglobin O 2 unloaded from hemoglobin during normal metabolism O 2 reserve that can be unloaded from hemoglobin to tissues with high metabolism Tissues during exercise Tissues at rest Lungs P O 2 (mm Hg) O 2 saturation of hemoglobin (%) Bohr shift: Additional O 2 released from hemoglobin at lower pH (higher CO 2 concentration) pH 7.4 pH 7.2 (a) P O 2 and Hemoglobin Dissociation at 37°C and ph 7.4 (b) pH and Hemoglobin Dissociation

Chapter 42: Gas Exchange 1.Why is gas exchange important? 2.How have gas exchange systems changed as animals evolved? 3.How have fish gills evolved for maximal gas exchange? 4.Why don’t gills work on land? 5.What adaptations do land animals have? 6.What is the flow of air in our respiratory system? 7.What is the difference between positive & negative breathing? 8.How is breathing controlled? (oxygen homeostasis) 9.How are gases exchanged? 10. How is the O 2 carried in the blood? 11. How is O 2 dumped from hemoglobin? 12. How does CO 2 travel from tissues to lungs? - Most dissolved in plasma as bicarbonate ion

Figure Carbon dioxide transport in the blood Tissue cell CO 2 Interstitial fluid CO 2 produced CO 2 transport from tissues CO 2 Blood plasma within capillary Capillary wall H2OH2O Red blood cell Hb Carbonic acid H 2 CO 3 HCO 3 – H+H+ + Bicarbonate HCO 3 – Hemoglobin picks up CO 2 and H + HCO 3 – H+H+ + H 2 CO 3 Hb Hemoglobin releases CO 2 and H + CO 2 transport to lungs H2OH2O CO 2 Alveolar space in lung To lungs Carbon dioxide produced by body tissues diffuses into the interstitial fluid and the plasma. Over 90% of the CO 2 diffuses into red blood cells, leaving only 7% in the plasma as dissolved CO 2. Some CO 2 is picked up and transported by hemoglobin. However, most CO 2 reacts with water in red blood cells, forming carbonic acid (H 2 CO 3 ), a reaction catalyzed by carbonic anhydrase contained. Within red blood cells. Carbonic acid dissociates into a biocarbonate ion (HCO 3 – ) and a hydrogen ion (H + ). Hemoglobin binds most of the H + from H 2 CO 3 preventing the H + from acidifying the blood and thus preventing the Bohr shift. CO 2 diffuses into the alveolar space, from which it is expelled during exhalation. The reduction of CO 2 concentration in the plasma drives the breakdown of H 2 CO 3 Into CO 2 and water in the red blood cells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4). Most of the HCO 3 – diffuse into the plasma where it is carried in the bloodstream to the lungs. In the HCO 3 – diffuse from the plasma red blood cells, combining with H + released from hemoglobin and forming H 2 CO 3. Carbonic acid is converted back into CO 2 and water. CO 2 formed from H 2 CO 3 is unloaded from hemoglobin and diffuses into the interstitial fluid